Inside valvegear in 7mm. Techniques and components

Steph Dale

Western Thunderer
I've built the odd set of valvegear in 7mm scale before and even two locos in 3.5mm that have it (don't ask... ::)).  But I'm aware it's a common aspiration for many modellers.  I'm in the process of brushing up my technique at the moment and am also looking at improvements to how I'm doing things.

Added to which I have just (as of ten minutes ago) finished assembling a crank-axle without the use of solder having heard some favourable reports on the behavior of some of the Loctite-branded adhesives.  I normally silver-solder the things, but in this instance I was pleased with the ease of assembly, lack of stress/drama and the fact that I won't have any cleaning up to do: the hardened flux from silver-soldering is itself a pain to shift.  I also made a test piece by fixing a spare brass bearing to an inch or so of 3/16" silver steel, which I look forward to hitting with a lump hammer sometime later this week.

So your best thoughts and tips please: what should we/I be watching out for as build progresses?  Has anyone else here put together a crank axle with Loctite?  How did it fair?

Steph
 

Dog Star

Western Thunderer
Steph,

How considerate of you to try this as I have to go in the same direction.  If you could just endeavour to make all of my mistakes / take all dead-end routes before me then I shall be very grateful for your efforts.

Being serious about this topic, you will recall that I posted the current situation in regards to a Slater's S7 axle for an O/F GWR 4-4-0.  I spent a couple of hours this weekend in discussion with a more experienced modeller who has offered to "concoct" a crank axle for the Bulldog which I wish to build.  Given that we have the Finney inside crank castings and some Slater's wheels (which will be bored through to remove the taper) then the result of the discussion is that the crank axle is going to have seven separate pieces plus eccentrics.  The inside cranks are going to be press-fit with pins and the outside cranks are going to be minimum clearance with either epoxy or cyano.  Am I worried that the outside and inside axleboxes will be trapped?  Yes.

Added to this, the rear coupled axle is going to be driven so that axle will carry the gearbox and shall therefore require either one or two telescopic joints.

At least the coupled axles are going to start as full-length (55mm) PGMS stock.

regards, Graham
 

Steph Dale

Western Thunderer
Graham,

I've got a notepad full of bright ideas, but figured it was time to try out those that relate to 'lessons learnt' from building inside valve gear before.  So that includes jigging the various parts so that the lengths of the rods are consistent.  Which having just made up the jig and one eccentric rod/strap assembly works well; and the jig is only made from 0.080" styrene and some 0.8mm wire, soldering takes place with a strip of aluminium baking foil in use to protect the (non-critical) area of the jig that might come in contact with the iron.

But, I must confess I'm starting easy.  Well relatively so.  This time it's a GWR 2251; the motion set using parts from both Finney and Griffin.  The crank axle is a conventional one and has been made so that the width across the outside of the cranks is 20mm.  There will have to be some joggles and or 'tricks' to keep the rods parallel and cope with the offset between the under-scale-width crank axle and the pretty-much-scale-width valveguides and slidebars.  But if my calculations are correct it will all fit...

From this the next loco is a LSWR/SR G6, this has single slidebars and a much more conventional layout of the Stephenson gear.  If my trials with the Loctite prove successfull, this loco will have splitaxles for all wheels as I will be able to make up an insulated crank axle.  As you may know I already have a few techniques for producing split axles on the bench; the 2251 will have them on the leading and trailing coupled axles.

Then I need to consider the Duke and other GWR 4-4-0s.  By then Slater's may have made their mind up about the new axles.  There is the thought in my mind that these offer a significant opportunity as, like you, I'm worried about trapping bearings and transmissions in place.  If the yet-to-be-introduced new GWR axles are a success then I would be building my Duke up using a length of tube between the face of the wheel hub and the back of the outside crank.  This would allow the screw in the end of the crank to be used to clamp the cranks and wheels in place.  For the sake of this opportunity I'm going to hold-fire on the Duke until I've seen what Slater's propose.

So; after the G6 I'll probably duck out from this thread for a bit; there's a batch of SR 'U's to be done by September next year...

Steph
 

28ten

Guv'nor
In my experience, loctite 601 (I need to check the bottle) and a pin is more than sufficient and it requires no clean up.    Personally I prefer split eccentrics as you can drop the valve gear which makes setup much easier, but it is an added complication.
I am sure Dikitriki will be along and I believe he has been using some castings for split eccentrics,
 
G

Graham Powell

Guest
The wheels on my 5 inch 2-6-0 steam engine are held on with Loctite 603. Just recently myself and a friend had to sleeve the axle pump and that was also put in with Loctite. Brass to brass it goes off in about 7 seconds and afterwards is immovable.  I have other engines where the wheels are held on with Loctite. Much easier than silver soldering.
rgds
Graham Powell
 

iploffy

OC Blue Brigade
I didn't realise we were talking about larger scale models when  I was a youngster I used to build 5" models and the axles where secured on using loctite and pins, that was until we decided to build a driving truck with disk brakes .It was decided that the amount of heat in the axle during braking loctite would not hold so it was Silver soldered instead that was fun cherry red and gently adding solder sticks.

Ian
 

Dog Star

Western Thunderer
Steph Dale said:
... the next loco is a LSWR/SR G6, this has single slidebars and a much more conventional layout of the Stephenson gear.

Hi Steph,

Please expand upon the comment above - specifically what you mean by "much more conventional" for I think of the GWR layout as being pretty conventional...

regards, Graham
 

Dikitriki

Flying Squad
Hi

I've turned up, but I thought we were all here to learn from Steph, not tell him what to do. ;D

I think you're very brave using glue. I'm sure it's going to be fine......probably......but I couldn't bring myself to do that. However I did not silver solder my crank axles, too much heat required and a sod to clean up (and I don't have any), so I used 'normal' solder and pinned the joints. I guess only time will tell how durable the glued approach is.

I do think you have to be able to drop the crank axle, which means devising some way of retaining the bearing (I used the loco springs screwed in) and springing the axle. On my Joys valve gear, which of course has no eccentrics, the rear of the connecting rod big end is screwed in, so all the valve gear is retained in the chassis. With Stephensons, nearly all of it can be withdrawn with the axle - I leave only the counterweights in situ. It probably depends on each individual loco as to where you can break a joint and how much has to be left in the chassis.

The Stephenson's valve gear I am working on at the moment is Sanspareil and the eccentric sheaves are split front and back, so can be attached after the crank axle is made, and made dismantleable if necessary. This contrasts with Laurie Griffin's approach where the eccentric sheaves are in one piece and must be fitted before the crank axle is soldered together - a high risk approach in my opinion.

I put some pictures of my valve gear here http://www.rmweb.co.uk/community/index. ... e__st__100
Joy's on P2, Stephenson's on P5. No recent entries as I have been working on the layout and fitting Dingham auto couplings to the stock. Gosh, aren't they fiddly to assemble and install?

I shall look forward to your thread Steph, always worth seeing what you are up to :thumbs:

Regards

Richard
 

Steph Dale

Western Thunderer
Graham,

Alright, I'll stick with 'a little more conventional'.  Suffice to say that there aren't many other railways that suspend the expansion link directly from the lift links: most use a 'saddle pin' which is bolted to the back of the expansion link.  The square valve guides seem to have been pretty unique to the GWR too.

In terms of the other issues/comments raised; I've just assembled my crank axle with Loctite 638.  This has at least twice the shear strength of 601 so I'm not expecting any failures.  I've also got half a thought that it'll be better when used to make up the insulated equivalent as the use of accelerator (required because of any non-metal parts) reduces the strength somewhat.  If in doubt refer to the manufacturer's data sheets...!

I'm looking at splitting the eccentric straps.  Laurie provides a few simple thoughts on how to do that with his components by drilling and using wire pins.  I know that on the locos where the back of the strap can't be seem I could just go with the wire on its own.

I really appreciate the replies and experiences gathered so far and welcome any further thoughts.  I'll post some pictures of the 2251 chassis/parts when they're ready for assembly.

Richard,
Thanks for the thought: a backhanded compliment if ever I got one ::) I hadn't thought of the dropping the axles thing as being particularly 'special' as it's something I make all my models do.  You're correct though; it's pretty much an imperative for a loco with inside motion.  In terms of the longevity of the Loctite, I'm pretty certain it'll do what I want it to; I could do the calculations to work out which is stronger I guess.  Nah, life's too short; good enough is good enough as the wise man said...

The 2251 will have to have split eccentrics as the valve spindles can't be removed from the guides.  For the G6 I'm wondering about leaving the eccentric straps in one piece, but am slightly worried about Loctite (or solder) running out and jamming the whole lot solid.  We'll see.  Gotta make a test piece for the insulated crank axle first.

Cheers,

Steph
 

28ten

Guv'nor
I agree with Richard about split eccentrics being far preferable, not just incase something gets gummed up but for troubleshooting. IMHO loctite is sufficient, the main problem in small scales is the tiny surface area, which is why I also pin the cranks. As for building it with split axles rather you than me  :)) :))
 

Dog Star

Western Thunderer
28ten said:
I agree with Richard about split eccentrics being far preferable, not just incase something gets gummed up but for troubleshooting.

The point which is made above is one which concerns me when considering the crank axle of a GWR Bulldog.  The basis of the model is a Finney kit along with the appropriate set of parts for the internal motion.  In the supplementary parts kit from Finney one gets the connecting rods / eccentric rods / expansion links as n/s etches, the eccentric sheaves as four, separate, turnings and brass castings for the cranks.  Each eccentric rod and strap is etched as a complete item...  and the two layer connecting rods (on assembly) have the bearing strap integral with the rod then if one assembles the parts as per the instructions then the connecting rods and eccentric rods are not removable from the crank axle....  along with the inside axle boxes, wheels and outside axle boxes.  There does not seem to be much leeway in respect to fit of parts or assembly thereof - I am not sure that my skills are adequate to get all of the bits in place first time!

I shall be very pleased to hear from anyone who has constructed an O/F engine with the internal motion.

regards, Graham
 

28ten

Guv'nor
I built a 3232 with the Finney parts and the problem I found was the general slop in the whole mechanism, there is nothing to physically stop any lateral movement of the gear and the whole approach owes more to the flexichas 'give it enough slop and it will work' ethos than any engineering principle! having said that it does work. Personally I prefer the split eccentrics and forked joints approach, with minimal slop/sideplay and nothing more than 1mm vertical movement in the axleboxes.
I should also say that with this whole lot permanently attached to the axle fitting and removal of the motion is not a five minute job  :headbang: and that is without outside cranks.  :eek:
Im sure you have MRJ 53 which has Tony Reynalds Atbara, and he appears to have the axle boxes permanently fitted and motion that is split which would seem to be the best route.
 

Dog Star

Western Thunderer
28ten said:
Personally I prefer the split eccentrics and forked joints approach.

So true... which of our supplies might offer the necessary castings for the internal motion as fitted to Dean engines?

regards, Graham
 

Steph Dale

Western Thunderer
I've taken on board the hints from here and will be splitting the eccentric straps (I did on the last set I made too). But for accuracy and consistency I came to the conclusion that the setting for length was best done before splitting the straps. So, as indicated earlier, here's the jig for setting the lengths of the eccentric rods. I have no doubt a variation could also be employed for those locos that had 'shaped' rods too...:

 

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Steph Dale

Western Thunderer
Time for a quick update methinks;

After breaking two 0.5mm drills in the process of trying to drill the eccentric straps such that the two parts can be pegged together, I went back to plan 'A'. I decided that the loss of drills and time was too costly. So I went for a slot and tab approach. The bosses on the straps were cut lengthways with a razor saw, the eccentrics split using a piercing saw and a strip of scrap etch soldered (with 224 degree) into the slots. When the time comes I'll apply a little flux and 144 degree solder to make them whole again:

 

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Dog Star

Western Thunderer
I am not able to see the images which have been posted recently, the post has large rectangles for the images - with a small white square top left and a red cross (plus the text ila rendered).  If I click on the box then I get a message that the file cannot be opened/found.

Advice anyone?

thank you, Graham
 

Steph Dale

Western Thunderer
Yep, I can see 'em too.  Look like rubbish to me; who is this clown...?
Oh.  Ahem.  ;D

Ian, Martyn,

Thanks for the comments.  Just a quick poll if I may: would you be happy/interested if components like these were available off the shelf from Laurie Griffin?  I'm doing some patterns for different variants of Stephenson valvegear and was wondering whether this approach would be acceptable (as an alternative to drilling/pinning, that is)?

For those who might be wondering, I'm currently looking at parts for the Southern and constituents: Drummond LSWR to start with...

Steph
 
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